more robust cpu detection

tools/rosmake/src/rosmake/parallel_build.py

@@ -47,15 +47,24 @@ import threading
 
 
 def num_cpus():
-  n = 0
-  cpuinfo_file = "/proc/cpuinfo"
-  if os.path.exists(cpuinfo_file):
-    for line in open(cpuinfo_file):
-      if line.startswith("processor"):
-        n = n + 1
-  else:
-    n = 1
-  return n
+  """
+  Detects the number of CPUs on a system. Cribbed from pp.
+  """
+  # Linux, Unix and MacOS:
+  if hasattr(os, "sysconf"):
+    if os.sysconf_names.has_key("SC_NPROCESSORS_ONLN"):
+      # Linux & Unix:
+      ncpus = os.sysconf("SC_NPROCESSORS_ONLN")
+      if isinstance(ncpus, int) and ncpus > 0:
+        return ncpus
+    else: # OSX:
+      return int(os.popen2("sysctl -n hw.ncpu")[1].read())
+  # Windows:
+  if os.environ.has_key("NUMBER_OF_PROCESSORS"):
+    ncpus = int(os.environ["NUMBER_OF_PROCESSORS"]);
+    if ncpus > 0:
+      return ncpus
+  return 1 # Default
 
 class DependencyTracker:
   """ Track dependencies between packages.  This is basically a